WordNet records no synonym and no antonym for proconsul. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
an official in a modern colony who has considerable administrative power
a provincial governor of consular rank in the Roman Republic and Roman Empire
an anthropoid ape of the genus Proconsul
Synonyms, antonyms and the broader and narrower relations for proconsul come from Princeton University’s WordNet. Full sources and licences.